Add substraction

Add a test scenario and the implementation for substraction. It is very similar to addition
Implementation of Multiply

Do the same thing as usual for multiply, two files had been modified s
ADD duplication

insert new process for duplication
add also other file : forth
Basic check for empty stack

add a new file to manage errors
Merge branch 'tp2' into stack_dup

add meaningful message
Add STACK system command
Merge branch 'stack_dup' into tp2

Conflicts:
	lua/forth